Call distributing system



Aug. l, 1939. J. wlcKs CALL DISTRIBUTING SYSTEM Filed Sept. 2O, 1957 2 Sheets-Sheet l l JOHN w|cKs BL i094 ATTORNEY.

Aug. l, 1939. J. wlcKs GALL DISTRIBUTING SYSTEM vFiled sept. 20, 1957 atented Aug. l1, 1939 PATENT OFFICE CALL DISTRIBUTING SYSTEM John Wicks, Oak Park, Ill., assignor to Associated Electric Laboratories, Inc., Chicago, Ill., a corporation of Delaware Application September 20, 1937, Serial N0. v164,639

19 Claims.

The present invention relates to a call distributing system, and is concerned more particularly with such s ystems of the above-named character as are used to provide increased trunking eiliciency between an A board in one manual eX- change and a B board in another manual exchange.

The main object of the invention is the production of a new and improved call distributing system utilizing primary and secondary selector switches to distribute the traic to available cord circuits at the B operators positions.

Another object is the production of suitable circuit arrangements whereby all of the cord circuits at a particular B operators position are made busy during the time required for her to set up a connection received over one of her cord circuits. With this arrangement, calls from A operators control the primary selectors to select idle secondary selectors in connection with cord circuits in other B operators positions during the time that the cord circuits at one of the positions have been busied.

Another object is the production of suitable circuit arrangements whereby the secondary selector switches are divided into groups and are controlled by means of a chain circuit common to the group, to preselect idle cord circuits only when a predetermined number of the idle secondary selectors in the group are standing on bank contracts connected to busy cord circuits.

'I'he foregoing objects together with others not specifically mentioned at this time will be best understood from the detailed description of the trunking layout and the operation of the various circuits.

Referring to the drawings, Fig. 1 is a schematic diagram showing the trunking arrangement between an A board located in one manual cnice and the B board located in another manual ofce, while Fig. 2 is a circuit diagram showing the apparatus required for a system of the type shown in Fig. l. Only such switching apparatus and circuits as directly concern the invention have been shown in detail in order to avoid unnecessarily complicating the description.

The general system of trunking from the A board in one manual office to the B board in the second manual office will rst be briefly explained. Referring to Fig. 1, the jacks at the A board, shown at the left-hand side of the drawing, represent only a portion of the jacks at positions 1 and 2. The jacks .IK-I, JK-Z, and JK--3 of the position 1 are connected to trunk lines T-I T-3, and I-5, respectively, while jacks .IK-I, JK-Z,

and JK-3 of position 2 are connected to trunk lines T-2, T-4, and T-6, respectively. These jacks are multiplied in a certain number of other positions of the A board asindicated by the diagonal line at the right oi the jacks. The trunk lines T-I to T-6, inclusive, are regular two conductor trunk lines extending between the telephone exchange in which the A board is located and the exchange in which the B board is located. These trunk lines are directly connected to pri-` mary selectors PS-I to PS-B, respectively, which switches are of the well-known rotary line switch type having a capacity of twenty-live lines out-l going irom each of their banks. The primary selectors are divided into groups, such as gro-ups 1, 2, and 3, and the trunks, such as II, I2, and I3, which represent a portion of the trunks from group 1, are multipled in the banks of all the primary selectors in group l and terminate in secondary selector switches, such as secondary selector switches SS-L SS-Z, and SS--3. Outgoing trunks I4, I5, and I6, which represent a portion of the trunks from group 2, comprising primary selectors PS-3 and PS-4, and are multipled in the banks of all of the primary selector switches in group 2. These trunks terminate in secondary selector switches, such as SS-ll, SS-5, and SS--G located in group 2 of the secondary selector switches. The primary selector switches in group 3, of which switches PS--S and PS-B are shown, are wired and multipled in the same manner described in connection with primary groups 1 and 2.

The trunks from secondaryselector switch SS-I are multipled in the banks of all of the secondary switches in group 1 and are terminated in an IDF. Only four of these trunks are shown, namely, trunks 20, 2 I, 22, and 23. The trunks, such as trunks 24 to 21, from secondary selector SS- are multipled in the banks of all of the secondary selectors in group 2 and are terminated in the IDF in the same manner as described in connection with the trunks of group l. Four positions of the B board are indicated at the right-hand side of the drawings, each of which shows lines indicating three of the plurality of cord circuits in each position of the B operators board. In order to distribute the traflic from the various groups of secondary selectors, trunks 20 to, 23, inclusive, are cross-connected at the IDF in such a manner that the trunk 2U is connected to the rst cord in the rst position of the B operators board. Trunk 2| is cross-connected to the first cord in the second position, trunk 22 is cross connected to the first cord in the third position, while trunk 23 is cross connected to the rst cord in the fourth position. The same is true of the trunks of group 2 of the secondary selectors, wherein trunks 24 to 21, inclusive, are cross-connected to cords 2 of positions 1, 2, 3, and 4, respectively, of the B board.

The foregoing explanation of the trunking arrangement is only considered between two offices in a manual system. There will necessarily be a similar system of trunking extending between the A board to each of the other manual ofllces as is the usual practice.

Fig. 2 shows jacks JK-I of A -board positions 1 and 2 connected to trunk Vlines T-l and T-2, respectively, which trunks terminate in the primary selector switches PS-I and PS-2, respectively, located in the same oflice with the B board. The primary selectors have access `to a plurality of trunk lines extending to a plurality of secondary selectors, such as SS-I and SS-2. However, only one of such trunk lines has been shown terminating in the banks of the primary selectors PS-I and PS-2. The secondary selectors, such as SS-I `and SS-2, have access to the trunk lines terminating in cord circuits, such as CC-l and CC-2, or position 1 of the B board. These trunk lines, only one of which is shown connected to the banks of each of the secondary selector switches, pass through an intermediate distributing frame, IDF, and are cross-connected to the cord circuits of the various operators positions in accordance with the traic conditions in the B board. Only such apparatus and circuits as are required to describe the invention have been shown and it `should be understood that any type of cord circuit can be used incorporating the modiiications shown on the drawings. The space shown between the two horizontal dash lines nearthe lower portion of the drawing indicates other primary and secondary selector switches of group 1, together with associated A board jacks and )B board cord circuits. The equipment shown below the bottom dash line is thecommon relay equipment at the B board.

The primary and secondary selector switches PS and SS of Fig. 2, are mechanically of the wellknown rotary type of switch of which the wipers haveno normal position and move in a forward direction only. Furthermore, the rotary switch mechanismv is of the type arranged to advance its wipers upon each deenergization of the operating magnet. v

It is believed that the foregoing brief descripvtion of the trunking arrangement between the A Vboard and onepmanual oice'and the B board in another manualoiiice is sufficient for a clear understanding of the general layout of the system.

The method of operation and the circuits involved will be Vfully described in the detailed specication, which is to follow.

As is well known in telephone practice, the straightforward method of trunking does not require the use of any order wire between an A ,board in one manual oflice and the B board in another manual oflice due to the fact that the conversation between .the two operators is carried on over the trunk selected by the calling A operator.

In order to explain the establishment of a connection between the manual A operator in'one .exchange and the B operator in another exchange, it will be assumed that the A operator at position 1, Fig` 2, has received a call from a subscriber who-desires rto extend a connection to a subscriber located in the exchange area served "magnet 235 in series.

by the manual office in which the particular B board is located. In addition, it will further be assumed that the operator in selecting a trunk to the wanted exchange has inserted the calling end of her cord circuit into the jack JK-I which jack is connected to the trunk line T--|. When the calling plug of the A operators cord circuit is inserted into the jack JK-|, a battery potential is applied to the sleeve of the jack, thereby energizing the sleeve relay 20|.

The energization of the sleeve relay 20| closes an obvious circuit for lighting the trunk lamp associated with the jack JK--|. Due to the fact that the conductors of the trunk line and the sleeve relay connected to the jack JK-l are multipled to other operators positions, the sleeve relays associated with the jacks at these multipled positions are operated and light their associated lamps to inform the operators at these positions that this trunk line is busy.

As a further result of the insertion of the plug of the cord circuit into the jack JK-l, a loop circuit is completed by way of the two conductors of the trunk line T-|, the normally closed contacts of armatures 204 and 205 of the primary selector PS-I, and the winding of the line relay 200. The A operators cord circuit is provided with the well-known supervisory relay, which is bridged across the tip and ring conductors of the cord circuit and is connected by" way of its two windings in series with line relay 206 over the above-traced circuit. However, due to the high resistance of line relay 206, the supervisory relay in the cord circuit is not energized,

but sufficient current vflows in this circuit to permit line relay 206 to energize.

The energization of relay 206, which is the line relayof the primary selecting switch PS-l terminating the trunk line T-I in the B board manual oilice, causes the initiation of the trunk selecting movement of this switch whereby an idle trunk extending to an idle secondary selecting switch is selected. Upon attracting its armature 208, re-

lay 206 completes a circuit including the winding of the switching relay 202 and the rotary At the same time this circuit is closed, the test wiper 2 Il is connected by way of armature `203 and its resting contact, `armature 201 and its front contact, to a -point midway between relay 202 and the rotary magnet 235. The operation now depends upon whether the test contact which the test wiper 2| I is in engagement with is busy or not. If this test contact is busy, there will be a ground potential applied thereto and the switching relay 2,02 willl be short-circuited in an obvious manner. At the same time the rotary magnet 235, being supplied with direct ground by Way of the test wiper 2|| and the engaged busy test contact, will begin operating to rotate the wipers 200, 2|0, and 2| I, step by step in search of an idle trunk line extending to an idle secondary selecting switch, such as SS-I. This automatic advancement of the wipers of a rotary switch of this type is the usual operation that takes place when its wipers are engaged with Vthe lcontacts of a trunk line which is busy. However, in the present case we may assume that when the operation of line relay 20h` of the primary selector switch PS--II takes place, its wipers are standing upon the contacts which are connected to trunk conductors 2|2, 2|3, and 2|4, as shown in the drawings, and we may also assume that this trunk line is idle at the same time.

AWhenthe circuit of the switching relay 202 is zompleted through the rotary magnet 235, under the above-assumed condition, the switching relay 202 will not be short-circuited and the rotary magnet 235 will not operate in series with the high resistance of the switching relay 202. 'I'he switching relay 222, however, is energized, with the following results: At the back contacts of armature 2Il3, it disconnects the previously described shunting circuit for the switching relay 202 and at the front contact of this armature, it connects ground potential from armature 208 to the test conductor 2H! of the trunk line eX- tending to the seco-ndary selector switch SS-I by way of the test wiper 2l I. Furthermore, this ground potential is also applied to the test contacts in the banks of the primary selector switches to which trunk conductors 2I2, 2I3, and 2ILl are multipled for the purpose of preventing other primary selector switches from seizing the trunk line which is now engaged by the primary selector switch PS-l. A further result of the grounding of conductor 2Ifl is to provide a temporary holding potential for the lower winding of the line relay 2lb in the secondary selecting switch SS-i- At the back contacts of armatures 2M and 225, switching relay 222 disconnects the two conductors of the trunk line T-i from the winding of line relay and at the front contacts of these armatures the trunk line is extended by way of wipers 2l'i9 and 2li) to they outgoing trunk line conductors 2 l2 and 2 I3. The line relay 23S in addition to being somewhat slow in energizing when its circuit is closed is also slow to release when the circuit through its winding is opened. Therefore, the ground potential applied to the test wiper 2li by Way of armature 208 is not disconnected until the secondary selector switch SS-I has had time to operate and select a` cord circuit in the B board.

It will be seen that the line relay 2l5 of the secondary selector switch SS-I is normally bridged across the line conductors 2I2 and 2I3 by way of the normally closed contacts controlled by armature 2H. Therefore, when the trunk line T-l of th A board operators position is transferred from the winding of the line relay 206 of the primary selector switch PS-I to the line conductors 2I2 and 2l3 by the operation of the switching relay 282, the upper Winding of line relay 2I5 is energized over a loop circuit including the A operators cord circuit. The upper winding of line relay 2id is of suiciently high resistance to prevent the operation of the supervisory relay in the A operators cord circuit. However, the line relay 2I5 energizes and closes the X contact of armature 2id, which contact closes before armature 2li' closes its front con-` tact to disconnect the circuit for the upper winding of relay 2iii. The ground potential applied to test conductor 2|@ now completes a locking circuit for the lower winding of relay 2I5, while at the normally closed contacts controlled by armature 2W, the line conductor 2I2 is disconnected from the upper winding of line relay 2I5 and connected by way of the front contact of armature 2 I'l to the wiper 222.

It may be well to mention at this timev that the secondary selector switches, such as SS--I and SS-2, are not accessible to the primary selector switches when the cord circuits that the'wipers of the secondary selector switches are engaged with, are busy. When the wipers of the secondary selector switch, such'as SS--l are engaged with a busy cord circuit, a ground potential is applied to the test conductor 2M by way of a l3 Wiper 224. For 'esamina wn the 6rd nella CC-I is engaged by another secondary selector switch, for example, the secondary selector switch SS-2, by way of the bank multiple wiring, ground potential is r'turned from armature 23| in the cord circuit @l-I, normally closed controlled by armature 254, jumpered to the trunk conductor 225 at the IDF, test wiper 224 of 4 the secondary selector switch SS-I, to test conductor 2 I4 and the multipled test contacts of the primary selector switches. This ground poten- 'tial applied to the test bank contacts accessible to the wiper 2Il of the primary selector switch prevents the seizure of secondary selector switch SS-l whose wipers are standing on bank contacts of a busy cord circuit. Accordingly, the primary selecting switch will automatically rotate its wipers in the previously described selfinterrupting circuit until its wipers engage a, trunk line extending to a secondary selector* switch whose wipers are standing on a trunk line of an idle cord circuit in the B operators switchboard It has been assumed in the description thus far of the operation of the secondary selector switch SS--I that its wipers are engaged with trunk line conductors 226-229, inclusive, of a cord circuit that is not busily engaged. Therefore, when the line relay 2I5 energizes and switches the trunk line conductors 2I2 and 2I3 through to the wipers 222 and 223, the circuit is further eX- tended by way of the bank contacts of these wipers, conductors 226 and 227, jumpers of the IDF, to the lower left-hand and right-hand windings of the repeating coil RI, to the upper and lower windings of line relay 233 in the cord circuit CC-L The supervisory relay in the A operators circuit which has been described previously as being bridged across the line conductors of the A operators cord. circuit is now included in series with the circuit of the upper and lower windings of relay 233 in the B operators cord circuit CC-I and both lower windings of the repeating coil Rf-I.

Relay 233 energizes over the above-mentioned circuit, but the supervisory relay in the A operators cord circuit does not energize at this time. Upon energizing, relay 233 closes a circuit for operating relay 232 at armature 237, and at armature 238 it completes a circuit for lighting the supervisory lamp 239 at the B operators position, thereby informing the B operator that the call is waiting on the associated trunk line. Due to the energization of relay 232, an obvious circuit is completed for relay 23D. At armature 23|, relay 230 applies ground potential by way of the normally closed contacts controlled by armature 25d, jumper on the IDF, conductor 223 and multiples thereof in the banks of the secondary selector switches, such as SS-l and SS-2, wiper 222 of the secondary selector switch SS-i, over two circuits in parallel. One of these circuits including the holding winding for relay 2l5, and the other branch of the circuit including conductor il i2 and multiples thereof in the banks of the primary selector switches, such as PS-l and PS--2, test wiper 2 I l, armature 283 and its iront Contact, winding of the switching relay 202, self-interrupting contacts and winding of the rotary magnet 235, to battery. The return of this ground potential from the cord circuit CC-l maintains the line relay 2| 5 and the switching relay 202 energized after the removal oi ground potential from armature 208 by the deenergization of line relay 20B.

It should be understood, however, that due to theA fact that the secondary selector switch SS-I is engaged with an idle cord circuit when the primary selector PS-| seized the trunk line conductors 2 I2, 2|3, and 2|4, that the time interval required for the return of ground on conductor 2|4 from the cord circuit CC-I to maintain the line relay of the secondary selector switch and the switching relay of the primary selecting switch energized is a comparatively short nterval. Whereas, if the secondary selector switch SS-I was ofthe type that would be required to search for an idle cord circuit in a B operators position after it has been seized by a primary selecting` switch, the return of ground potential from the idle cord circuit found by the secondary selector SS-I would be of considerably greater interval and may be of suiiicient length of time to permit the line relay 206 of the primary selector switch to fall back and remove ground potential from the switching relay 202 and the line relay 2|5 before ground potential is returned from the seized cord circuit. This would result in the deenergization of both the switching relay 202 and line relay 2 i5.

As a further result of the operation of relay 230 in the cord circuit CC--|, the ground potential applied at armature 23| is also extended by way of the IDF and conductor 229 and multiples thereof in the secondary selector switches SS-i and SS-Z, wiper 225 of the secondary switch SS-L winding of relay 2 i8, to battery. Therefore, as a result of the seizure of cord circuit CC-I by the secondary selector switch SS-L ground potential is returned from the seized cord circuit to maintain the line relay 2|5 of the secondary selector switch SS-I and the switching relay 202 of the primary selector PS-I energized and also to complete an energizing circuit for relay 2 I8 of the secondary selector switch SS-|. The operations performed due to the energization of relay 2 i3 will be described hereinafter.

The cord circuit CC-l at the B operators position has now been automatically connected to the trunk line selected by the A operator and the B operator attending the group of trunks in which the cord circuit CC-| is located is connected with the seized cord. The B operator may be automatically connected to the seized cord circuit, or she may be manually connected by a key when she responds to the lighting of lamp 239. The type of'cord circuit that is used is of no interest in the present invention and only a portion of the cord circuit has been shown. The dash lines in the line conductors connected to the plug P-l of the cord ycircuit CC-|, representing that part of the cord circuit which has not been shown. In any event, as soon as the B operators telephone instrument is connected with the trunk seized by the distant A operator, a tone signal is automatically transmitted to the A operator to indicate that the B operator is now connected and is ready to receive the number of the wanted subscriber located in her exchange area. When the B operator has received the number of the desired line she tests the called subscribers line jack in the usual manner and inserts the trunk plug P-I in order to complete the connection. The ringing of the called subscribers telephone may be accomplished in any of the well-known ringing schemes by either automatic or manual operation.

When the called subscriber answers, the ringing current is disconnected from the called line in the usual manner which is of no interest in the present invention, and in addition, relay 234 isoperated. At armature 262, relay 234 places a shunt circuit around the high-resistance winding of relay 233. In addition, at armature 26|, relay 23.4 causes the supervisory lamp 239 to be extinguished. As a result of the shunting of the highresistance. winding of relay 233, the supervisory relay in the A operators cord (not shown) receives sufficient current flow in its windings to cause the relay to operate and thereby eX- tinguishes the calling supervisory lamp in the usual manner. Therefore, the answering of a call by the wanted subscriber in the manual oice containing the above-mentioned B board, gives the originating Aoperator the supervisory signal.

' The extinguishing of the trunk line supervisory lamp 239 is described in the present instance as being responsive to the answering of the called subscriber. However, in some cases the B operator does not receive a signal when the called subs criberA answers a call, the trunk lamp at her position responding only to the A operators seizing oi a cord circuit or disconnecting therefrom.

The connection is now completed between the calling subscriber in the area served by the manual office at which the A board is located and the called subscriber served by the manual oiiice in which the B board is located. The talking conductors of the circuit shown in Fig. 2 include the trunk line T-I, armatures 204 and 205, the associated front contacts of relay 202, wipers 209 and 2|0, conductors 2 |2 and 2|3 of the secondary selector switch SS-l, front contact controlled by armature 2|1, wipers 222 and 223, conductors 226 and 221 cross connected at the IDF to the lower winding of the repeating coil R-l. The battery feed for talking purposes being connected to this circuit in the A operators cord. The called end of the talking connection is completed through the upper winding of the repeating coil R,-|, and the tip and ring conductors connected to the plug P-I. The talking current for this circuit being connected in the B operators cord circuit equipment (not shown).

Referring again to the seizure of the cord circuit CC-I by the A operator and the resulting transmission of a tone signal to the A operator to indicate to her that the B operator is connected. At this time the common equipment associated with position 1 at the B board, is also controlled and ground potential is applied to conductor 259 causing the operation of relay 253. Accordingly, when the B operator at position 1 is idle, any one of the cord circuits at her position is seizable' by an A operator. It is understood, however, that if a call is set up over any one of the cord circuits in the B operators position, a ground potential is applied to test conductors, such as 228 and 229 by way of armature 23| of the operated relay 230. This relay is maintained energized throughout the entire connection established over any one of the cord circuits. When a connection is set up over a cord circuit, such as cord circuit CC-|, the operator is again available to receive ano-ther call over any other cord circuit.

During the interval required for the B operator to receive the wanted subscribers number and also to set up the connection to the wanted subscribers line, provisions are made in the cornmon equipment of the particular B operators position for busying` all the remaining cord circuits at her position until she is again available to establish further connections. This is accomplished as mentioned above, by the grounding of conductor 259 during the time she is answering and settinguup a call receivedover oneof her cord circuits. The armatures 254 and 255 controlled by relay 253, are shown connected to the test conductors 223 and 255, respectively, while armature 255 is drawn to represent the remaining cord circuits at position 1 of the B operators board. When relay 253 is operated, armatures 254, 255, and 256 and any other of such armatures of other cord circuits (not shown) at position 1 are all operated to engage their associated front contacts and to disengage the normally closed contact controlled by the front contact of these armatures. In the cord circuit CC-|, the ground at armature 254 is connected by way of its front contact of conductor 228 and since this cord circuit is the one that'has been used in establishing the above-described connection, the ground potential at armature 254 is merely substituted for the ground potential applied by Way of armature 23| to maintain the line relay 2|5 of the secondary selector SS--l and the switching relay 252 of the primary selector PS-I energized. However, at armature 255 of the cord circuit CC-2 of position l, (relay 232 is not energized due to the fact that this cord circuit is not in use) ground potential is applied by way of test conductor 265 to the banks of the secondary selector SS-2 and all other secondary selectors in the group having access to the cord circuit (3C-2 by way of the bank multiple. This ground potential applied to test conductor 265 prevents a primary selector from seizing an idle secondary selector whose wipers are engaging the busied cord circuit, due to the fact that the ground potential is then extended through the connected test wiper, such as 224', to a test conductor, such as 2|4, in the banks of the primary selector switches, it being understood that armature 255 and all other armatures similar to armature 256 of the remaining cord circuits at position 1 of the B operators board also apply ground potential to the test banks of the secondary selector switches having access thereto.

Referring again to relay 2| 8 of the secondary selector switch SS-L it will be noted that when all of the secondary selector switches in a group are idle that a chain circuit is normally completed from ground at armature 220, resistance 236, resistance 236 of the secondary selector switch SS-2, and in series with similar resistances of all the remaining secondary selectors in the same group, through the winding of marginal relay 244, to battery. Due to the total resistance in this chain circuit, relay 244 does not receive suiiicient current to energize. Attention is called to the fact that each group of secondary switches is provided with a similar series circuit for a marginal relay, similar to marginal relay 244, the functions of which will be apparent from the following description.

It will be recalled that when the cord circuit CC-I was seized by secondary selector switch SS- L that ground potential was returned on conductor 229 and multiples thereof, to cause the -energization of relay 2|8. Therefore, if the wipers of several of the secondary selector switches in the same group are also Vstanding on bank contacts to which the conductors of cord circuit CC-l are multipled, the relays, such as relay 2|8, in such secondary selector switches are also energized from the same ground potential returned over conductor 229. At armature 2li), relay 2|8 prepares a circuit for the rotary magnet 22|, and at armature 22d it shunts out the resistance 235 of the `chain circuit for the marginal relay 244.

S It wiunow be assumed that the wipers 222' to 225 of the secondary selector switch SS-Z are standing on the bank contacts to which the conductors 226-229 of the cord circuit CC-I are multipled Therefore, the ground potential returned on conductor 229 and multiples thereof by the cord circuit CC-I causes the operation of relay 2|8 of the secondary selector switch SS--2. Relay 2 l upon energizing prepares a similar circuit for its rotary magnet 22| at armature 2|9, and at armature 220 it shunts out the resistance 222 of the chain circuit for marginal relay 244. It will be apparent from the above description that any other secondary selector switches in the group, having their Wipers resting on the bank contacts to which the trunk conductors of the cord circuit CC-l are multipled, the relays corresponding to relays 2|8 and 2|8 will be energized and prepare the circuits for their associated rotary magnets and also shunt out resistances, similar to resistances 236 and 235. When suiiicient of these resistances have been shunted out of the chain circuit for the marginal relay 244 suflicient current will flow through the winding of the relay to cause it to energize. Attention is called to the fact that the ground potential returned from the cord circuit CC-| over the conductor 229 and multiples thereof to cause the operations of relays, similar to- 2|8, of all secondary selectors whose wipers are standing on l the trunk multiples of the cord circuit, is also returned over conductor 228 and multiples thereof in the banks of all they secondary selectors in the group. In the secondary selector switch SS-I, the one over which the call is extended, this ground potential provides a holding circuit for the line relay 2 I 5 and the switching relay 202, as has previously been mentioned, Whereas in the secondary Selectors over which no calls are extended and whose wipers are standing on the trunk multiples of the cord circuit CC-I, this ground potential is extended by Way of wipers, similar to wiper 224 of secondary selector switch SS-2, and conductors, similar to conductor 2|4, to the banks of primary selector switches, similar to primary selector switch PS--2. This ground potential is returned on conductor 2|4 and all similar test conductors of other secondary selector switches in group 1 to busy these secondary selector switches in the banks of the primary selector switches having access thereto.

In order to prevent the primary selector switches from having to search over too many busy bank contacts, the above-mentioned chain circuit for the marginal relay 244 is provided to reset the idle secondary selector switches that are standing on bank contacts of busy cord circuits to pre-select idle cord circuits so that the primary selectors will not have to search any appreciable time to nd an idle trunk line extending to a secondary selector switch and cord circuit.

Referring again to the operation of the marginal relay 244, it willbe noted that at armature 245 it completes an energizing circuit for relay 24E). Relay 240, upon energizing, closes the :front contacts of armatures 24|, 242, and 243, and all similar armatures of other secondary selector switches in the same group. Due to the fact that line relay 2|5 of secondary selector switch SS-l is energized, the closing of armature 24| has no effect upon the rotary magnet 22| because the circuit is opened at armature 2|6 and its back Contact. At armature 242, however, the ground potential applied to conductor 2 I4 by Way of 'test wiper 2-24' which isassumed to be standing .on bank contacts to wwhich the Abusy cord circuit CC-I is a multiple, completes a circuit for the rotar-yimagnet 22| by way of armature 2 I9 of the energized relay 2I8'. Rotary magnet V22| interrupts its own circuit and advances its wipers 22| to 225 one step to the -next vbank contact. If the cord circuit connected to the next bank contact is idle, the ground potential is removed from the wiper 224 and the wiperscome to rest on the cord circuit connected to these bank contacts. If the cord circuit kconnected to this bank contact is busy, a ground potential will be encountered by the .test wiper 224' and cause the rotary magnet to again energize and advance the Vwipers another step. In this manner, the secondary selector switch-SS2 advances its wipers until lan idle-.cord circuit is found, thereby .preselecting an idlecord circuit so .that it is available to a primary selector switch. Armature 243 and all other'armaturessimilar to armature 243, of other secondary selector switches close the above circuit describedin connection with secondary selector switch .SS-2 and 4accordingly control these secondary selector switches to preselect an idle cord circuit.

When the wipers -of `the secondary selector switch SS-Z have'been advanced to an idle cord circuit, relay 2 I8 deenergizes and opens the stepping circuit for the 'rotary magnet at armature 2I9 and removes the shunting circuit for resistance 236 at armature 229. The remaining secondary selector switches that have advanced ltheir wipers to idle cord circuits are also controlled in the'samemanner described in connection with selector switch SS-2. In this vmanner, resistances are Vagain -inserted in the chain circuit for the marginal relay 244 and the relay eventually falls back-and opens the circuit for relay 240 at armature Y245. Relay-240 falls back vand opensthe circuits elo-sed at the front-contacts of armatures 24|, A242, and `243 and all other similar Aarmatures of other secondary selector switches (not-shown).

It may be well tomention at this time that as long as the B operator 'at position 1 is busily engaged in setting up a connection ofthe type previously described over a cord circuit 'CC--L the energization of relay 253 which busieslall of the cord circuits at 'her position, vdoes not prevent'the secondary selector switches -such as SS- 2, -from selecting a cord circuit at herpositionwhen their wipers are automatically rotated to preselectan idle cord circuit. The temporary busying of the cord circuits at the B operators position that is extending a connection -is only for the purpose of preventing a primary selector -from'extending a call to her position while `she is busy. This arrangement Ycauses the primary selectors to rotate and find `an idle cord circuitat another B operators position. However, as soon as the B operator has completed the connection, referred to above, relay 253 `restores to normal and removes the busying potential from the cord circuits at her position that are available for additional calls.

Referringagain to the connection established overccrd `circuit CC-l, it will be remembered that when the called subscriber answered the supervisory Vlamp 239 was extinguished. When the conversation is completed between the calling :andi-the called subscribers, the hanging up of the called'subscriber causes the relay .234 to fall back. At armature 262, relay234 removes the shunt from around the .high resistance lower `winding of relay 233. Due to the fact that the high resistance of the lower winding of relay 233 is again inserted `inthe loop circuit including the lower Ywindings of the repeating coil Rl and the supervisory relay inthe A operators oord circuit, the supervisory relay in the A operators cord circuit deenergizes and lights the supervisory lamp at her position to give the disconnect signal. In addition, the hanging up of the calling subscriber lights the answering lamp at the A operators position, thereby informing her that the conversation between the calling and the called subscriber' has 'been terminated. In the B operators position the trunk lamp 239 is lighted when the called subscriber hangs up and relay 234 vis released, to indicate to the B operator that vthe called subscriber has hung up his receiver and the-connection'is about to be taken down b-y the A operator. However, it is to be understood uthat this is a representation of one type of supervision for the B operator and that in other types "of cord circuits the B operator does not receive any supervision 'on the hanging up of the called subscriber, but only receives `disconnectsupervision when the Aoperator pulls down the connection.

The -A operator takes down the connection by removing the plug of lher cord circuit from the jack .IK-1, thereby releasing the sleeve relay 29! and all othersleeve relays of jacks to which thetrunk line T-l is multipled. The release of the ysleeve relays extinguishes the lamps at all the 'positions to which this trunk line is multi pled to indicate to the operators. at these positions that this trunk line'is again available for the extension of calls. When the connection is broken down by removal of the plug by the A operator, relay '233 in the cord circuit CC-I falls back `andiextinguishes the lamp 239. At armature 231, relay 233 opens the circuit for relay 23"-2 which relay, upon falling back, opens the circuit for relay 239. When the B operator receives the disconnect signal she removes her plug Pl from the calledsubscribers line jack. The release of relay 230 removes ground potential from conductors'228 and 229 and multiples thereof'in'the banks of 'the secondary selector switches. When ground is 'removed from `conductor 229, relay 2H) falls 'back and again inserts the resistance 23S in the chain circuit of the marginal relay 244. The removal'of ground from conductor `229, wiper 224, and conductor EI-i, permits line relay v215 of the `secondary selector switch SS-l to restore to normal and in addition removes the holding ground from the switching relay 292. The deenergization of relay 2l5 restores the secondary selector switch SS-I to 'normal and the deenergization of switching relay 202 restores the primary selector switch PS-l vto normal. The trunk 'line and cord circuit T-I and CC-I, respectively, together with the primary `selector vPS--l and the secondary selector `SS-l, are now available for the extension of other calls.

A description willnow be given of the redistribution of secondary selector switches to preselect idle cord circuits when one of the positions of the B operators switchboard is vacated for any reason whatsoever. When an operator leaves her position, ground potential is applied to conductor 260 of the common equipment at her position, causing the operation of relay 248. At armature 249, relay 248 places a ground potential on conductor 229, and in addition, by way of the normally closed contacts controlled by armature 254 it places a ground potential on conductor 228. At armature 255, relay 248 places ground potential on conductor 266, and by way of the normally closed contacts controlled by armature 255 it places ground potential on conductor 255. This ground potential is extended by way of the multiples of these conductors to other secondary selector switches in the group in which selector switches SS| and SS-Z are located. In addition, armature 25| and all other armatures similar to armature 25|, of the cord circuits not shown in the drawings, extend ground potential to the banks of the associated secondary selector switches in the same manner as described in connection with armatures 249 and 252 of cord circuits CC-l and CC-2. In the secondary selector switch SS--I relay 2|8 is energized due to the fact that its wiper 225 is standing on the bank contact to which grounded conductor 229 is connected. In addition, the ground potential applied to conductor 228 is eX- tended by way of wiper 224 to conductor 2|4. The energization of relay 2|8 prepares a circuit for rotary magnet 22| at armature 2|9 and shunts the resistance 236 from the chain circuit of the marginal relay 224 by the closing of armature 22B and its front contact.

In the secondary selector SS-2 the wipers 222' to 225', inclusive, are shown standing on the rst set of bank contacts. It will be assumed, that the trunk conductors 226 to 229, which are connected to the rst set of bank contacts of the secondary selector switch SS|, are also multipled to the first set of bank contacts of the secondary selector switch SS-2. This being the case, the ground potential applied to conductors 228 and 22S is extended to the bank contacts upon which the wipers 224' and 225' of the sccondary selector switch SS--Z are standing. Therefore, the relay 2|8 is energized and the conductor 2|4' is grounded. The energization of relay 2|8 prepares a circuit for the rotary magnet 22|' at armature 2|9', and at armature 222' the resistance 236' is shunted from the chain circuit for the marginal relay 244.

The operation of armature 256, responsive to the energization of relay 248, applies ground potential to conductors 265 and 268 and multiples thereof terminating in the banks of the secondary selector SS-2 and other secondary selector switches in the same group of switches in which the secondary selector SiS-2 is located. Inasmuch as the wipers of the secondary selector switches SS--l and SS--Z are not standing on the bank contacts to which these conductors are multipled, nothing occurs in these two selector switches. However, it may be assumed that other selector switches in the same group have wipers standing on bank contacts to which these conductors are multipled, in which case, the relays, similar to relay 2W', located in these secondary selectors are operated in the same manner as described in connection with the operation of relay 2|8 of secondary selector switch SS-i and relay 2|8 of secondary selector switch SS-2. The operation of these relays will cause the resistances, similar to resistances 236 and 23E', to be shunted out of the chain circuit for the marginal relay 244 and in addition, will prepare the energizing circuit for their respective rotary magnets, similar to rotary magnets 22| and 22! As has been previously described, the shunting of the resistances in the chain circuit for the marginal relay 244 eventually causes the relay to Aoperate and complete the energizing circuit for relay 240. Relay 240, upon energizing, closes the front contacts of armatures 24|, 242, and 243, and all similar armatures. When the front contact of armature 24 is closed, the ground potential applied to conductor 2|4 is extended by way of armature 2lb` and its resting contact, armature 24| and its front contact, armature 2|9 of the energized relay 2|8, self-interrupting springs and winding of the rotary magnet 22|, to battery. In addition, the closing of front Contact of armature 242 extends the ground potential applied to conductor 2 I4' by way of wiper' 224' and the bank multiple connected to conductor 228, by way of the lower armature and resting contact of relay 2|5', armature 242 and its front contact, armature 2|9' and its front contact, self-interrupting springs and winding of the rotary magnet 22E', to battery. The ground potential applied to conductor 265 and multiples thereof of other secondary selector switches, similar to SS- 2, will also cause the operation of the rotary magnets of any of the secondary selector switches (not shown) having their wipers` standing on bank contacts to which this trunk conductor is multipled. It should be understood, however, that the wipers of some of the secondary selector switches, in the group of selector switches referred to above, may be connected to bank contacts terminating cord circuits in other positions of the B board, in which case, the test wipers, similar to wipers 224 and 225, are not grounded. Consequently the relays similar to relay 2|3, are not energized, and the operation of armatures, similar to 243, will have no eiect when such a condition is encountered.

The rotary magnets of the secondary selector switches in which the relays, similar to relays 2 l 8 and 2&8', are energized, advance their wipers until they engage idle cord circuits.

As soon as the rotary magnet 22| of secondary selector switch SS--I has advanced its wipers 222-225, inclusive, to a set of bank contacts to which an idle cord circuit is connected, relay 2| 8 is deenergized and opens the rotary magnet circuit at armature 2li) and again connects the resistance 23B in the chain circuit of the marginal relay 244. The wipers 222-225', inclusive, of secondary selector switch SS-2, which is controlled by the rotary magnet 22|', may not have found an idle cord circuit as soon as the wipers of the secondary selector switch SS-l. If other secondary selector switches in the same group in lwhich secondary selector switch SS-l is located have advanced their wipers and have found idle cord circuits, suilicient resistance may be again inserted in the chain circuit for the marginal relay 244 to cause the same to fall back and open the circuit of relay 24|). This may occur when the wipers of the secondary selector switch SS-2 are still standing on the bank contacts of a trunk connected to one of the cord circuits of a vacated B operators position.

It will be assumed, for the purpose of describing such a condition, that the wipers` 222' to 225', inclusive, have been advanced to the set of bank contacts to which conductors 2&3 to 256, inclusive, are connected when the marginal relay 244 and relay 24|] are deenergized. In the secondary selector switch SiS-2, relay 2|8 will be maintained energized from the ground potential applied at armature 255 and the conductor 2|4' will be grounded from the same source. The circuit for rotary magnet 22|', however, will be opened at armature 242 due to the fact that the relay 24|] has restored to normal. Therefore,

the wipers of the secondary selector switch SS--Z will come to rest in engagement with a busy cord circuit of a vacated B operators. position. However, the ground potential applied to conductor 2|4 and multiples thereof in the banks of the primary selectors, prevents the primary selectors from seizing the secondary selector switch SS-Z as long as conductor 2|4' is grounded. Inasmuch as the secondary selector switches` in the group shown on the drawings have been advanced and have preselected other cord circuits at B operators positions that have not been vacated, the fact that a few of the secondary selectors in the group are still in engagement with cord circuits extending to the vacated B operators position does not create any congestion in trunking, due to the fact that the primary selectors will have sufficient outlets to cord circuits of the attended B operators positions.

From the foregoing description of the busying of all the cord. circuits at a vacated B operators position, it will be understood that the secondary selector switches having access to these cord circuits will not preselect any of them as long as the cord circuits are busied by the operation of the relay248. Therefore, the calls that vhave previously been extended to these vacated B operators positions will now be redistributed amongst the remaining B operators at the switchboard. If some of the secondary selector switches are still positioned with their wipers engaging the busied cord circuit of the vacated operators position, the primary selector switches will be unable to seize these secondary selectors due to the fact that the test conductors, similar to 2|4 and 2 |4, will have a ground potential applied to them. It should also be understood that if the B operators position is vacated for any length of time, that the secondary selector switches having access to these cord circuits will eventually preselect idle cord circuits in attended B operators positions. Therefore, when the B operator returns to the vacated position and is ready to again extend calls through her position, no calls will be coming in to her position due to the fact that the secondary selector switches have preselected idle cord circuits in the remaining B operators positions. To eliminate any delay in again having calls distributed to the vacated position when it is again made available, the circuit arrangement about to be described is provided to redistribute the trailic to the now attended B operators positions.

It will be remembered that when the B operator vacated her position that relay 248 was energized over a circuit including conductor 260 and in response to the energization oi relay 248, in addition to bu-sying all of the cord circuits at the B operators position by closing armatures 249, 250, 25|, and other similar armatures not shown, slow-to-release relay 2'46 is energized from ground by way of the front contact of armature 252. When the absent B operator returns to her position she causes ground potential to be removed from conductor 260, thereby opening the energizing circuit to relay 248. Relay 248 restores to normal and removes the busy ground potential from all the cord circuits at her position and at armature 252 and its front contact opens the energizing circuit for relay 246. However, due to the fact that relay 246 is somewhat slow to release, a circuit is now completed by way of the back contact of armature 252, front contact of armature 2`4'|, through the winding o relay 265 which accordingly energizes. At-

tention is called to the fact that relay 265 is common to all B operators positions and is operated in the manner described above from any position that has been vacated and again put into operation by the return of the operator. At armature 266, relay 265 completes an energizing circuit for relay 24D which relay is common to all secondary selectors in group l. At armature 261 and similar armatures (not shown) relay 265 completes energizing circuits for relays, similar to relay 240, individual to each group of secondary selector switches. Responsive to the energization of relay 240, at armatures 24|, 242', 243, and all other similar armatures of the secondary selector swiches in the group including SS-I and SS-Z, it prepares a circuit for each of the rotary magnets of these secondary selector switches in the same manner as has been previously described. It will be remembered that in the previous description of operation that takes place when the B operators position is vacated, that the rotary magnets of the secondary selectors were automatically operated in order to select idle cord circuits in other B positions. In addition, it was also pointed out that some of the secondary selector switches may still be connected to cord circuits oi vacated B operators positions.

1t will be assumed in the present description, however, that some of the secondary selectors of the group have preselected other cord circuits than those connected to the vacated B operators position, and that other secondary selector switches in the group are standing on busy cord circuits, and have not been advanced due to the fact that suiiicient of the resistances, similar to resistances 236 and 236 have not been shunted out of the circuit of the marginal relay 244. The secondary selector switches that have their associated test wipers, similar to wipers 224 and 225, standing on bank contacts grounded by some cord circuit being used in extending a connection, will have a relay, similar to relay 2|8, energized and their line relays will not be energized. It is understood, however, that if any secondary selector switch is being used in the extension of a call that the line relay, similar to line relay 2'I5 will be energized and be locked up by way of its lower winding to the grounded test conductor, similar to conductor 2|4.

Assuming that some of the selectors are standing on busy contacts and the line relays are not energized, the previously traced interrupting circuit for each rotary magnet (completed by the energization of relay 240) and will advance the wipers step by step until idle cord circuits are found. When an idle cord circuit is found, ground potential will not be encountered on the test bank contacts and the test relay, similar to 2|8, will fall back and open the rotary magnet circuit. Since the cord circuits at the vacated B operators position are again available, some of the secondary selector switches select idle cord circuits in this position.

Shortly after the above-described deenergization of relay 246, slow-to-release relay 246 also falls back and again opens the circuit for relay 246 common to secondary group 1, and all other similar relays common to other secondary groups. Relay 240 falls back and opens the front contacts of armatures 24|, 242, 243, and all other similar armatures for controlling the automatic stepping of secondary selector switches in group 1.

In'the description thus far we have assumed that the cord circuits, such as CCI-'"-I and CC-2, are located in position 1 of the B operators board. However, it should be clearly understood that the cord circuits at position 1 may be cross-connected at the intermediate distributing frame IDF so that all groups of secondary selectors have access to cord circuits in this position. Therefore, when a B operator vacates a position, a relay, such as 248, is energized as previously described to busy all of the cords at the vacated position. When the B operator returns and causes the release of the relay, such as 268, a slow-to-release relay, such as 246, completes a circuit for the common relay 2i5. The diagonal line shown to the right of the relay indicates that this relay is common to all B operators positions. In response to the energization of relay 265, a circuit is closed at armature 266 for energizing relay 240, which relay is common to the group of secondary selector switches shown on the drawings. In addition, at armature 257, relay 255 completes a circuit for a relay, similar to relay 24B, in the next group of secondary selector switches. It is to be understood that relay 265 may have other armatures on its spring assembly whereby ground is extended to control relays, similar to relay 24D, of additional groups of secondary selector switches in which any of the cord circuits of the Various B operators positions are accessible.

In addition, it will be understood that marginal relays are also connected, in the same manner as relay 244, to their respective groups of secondary selector switches. When any one of the marginal relays is operated due to the shunting out of sufficient resistances, such as 236 a relay, such as 2M), is energized, thereby controlling the automatic stepping of the secondary selector switches of its group that have wipers standing on bank contacts of busy cord circuits.

From the foregoing description it is seen that the present invention makes it possible to secure eicient distribution of calls from an A operators switchboard in one manual exchange to a B operators position in a manual switchboard in a second exchange.

Having fully described the invention, what is considered new and is desired to have protected by Letters Patent will be pointed out in the appended claims.

What is claimed is:

l. In a telephone system, a plurality of trunk lines connected to multiple jacks in a plurality of A operators positions, a rst group of automatic primary trunking switches in which said trunk lines terminate, a second plurality of trunk lines connected to different multiple jacks in said plurality of A operators positions, 'a second group of automatic primary trunking switches in which said second plurality of trunk lines terminate, a first and second group of automatic secondary trunking switches, an individual secondary trunk line terminating in each switch of said groups of secondary switches, theindividualsecondarytrunk lines terminating in switches of said lrst group of secondary switches accessible to all of the switches in said rst primary group, the individual secondary trunk lines terminating in switches of said second group of secondary switches accessible to all of the switches in said second primary group, a B operators switchboard comprising a plurality of positions, a plurality of cord circuits for each of said positions, an individual trunk line for each of said cord circuits, one of the cord circuits at each one of said B operators positions accessible by way of its ndi- 9 vidual trunk line to all of the switches in the iirst of said secondary groups, and another one of the cord circuits at each one of said B operators positions accessible by way of its associated trunk line to all of the switches in the second of said secondary groups.

2. In a telephone system, a first and a second manual oiiice, inter-office trunk lines connecting said oces, a plurality of A operators positions at said .first oflice for receiving and extending calls to said second olce, a plurality of B operators positions at said second oice for completing incoming calls from said first office, primary and secondary selector switches at said second Office, said primary switches terminating the trunk lines from said iirst office, cord circuits at each of said B operators positions, said secondary switches having access to and means for preselecting said cord circuits, means in said primary switches operated responsive to the seizure of one of said inter-office trunk lines by one of said A operators for automatically selecting an idle cord circuit preselected by any one of said secondary switches.

3. In a telephone system in which straightforward trunking is provided to extend calls from A operators positions in one manual exchange to B operators cord circuits in another manual exchange, primary and Secondary selector switches at the exchange in which said B operators switchboard is located, trunk lines extending between said exchanges seizable by the A operators to extend calls, said trunk lines terminating in said primary selectors, means in said primary selectors operated responsive to the seizure thereof by an A operator over any one of said trunk lines for extending the trunk line used through said seized primary selector to one of said secondary selectors to seize the same, said secondary selectors having access to said B operators cord circuits, and means in said seized secondary selector operated responsive to the seizure thereof for extending the said trunk line through said seized secondary selector to an idle cord circuit of one of said B operators positions.

4. In a telephone system in which straightforward trunking is provided to` extend calls from A operators positions in one manual exchange to B operators cord circuits in another manual exchange, primary and secondary selector` switches at the exchange in which said B operators switchboard is located, trunk lines extending between said exchanges seizable by the A operators to extend calls, said trunk lines termipatins in Said primary selectors, means in said primary selectors operated responsive to the seizure thereof by an A operator over any one of said trunk linesfor extending the trunk line used through said Seized primary selector to one of said secondary selectors to seize the same, said secondary selectors having access to said B operators cord circuits, means in said seized secondary selector operated responsive to the seizure thereof for extending the said trunk line through said seized secondary selector to an idle cord circuit of one of said B operators positions, and means in said seized primary selector for preventing any other of said primary selectors from being operated to seize the same secondary selector used to extend the said trunk line to an idle cord circuit and for maintaining said secondary selector in seized condition.

5. In a telephone system in which straightforward trunking is provided to extend calls from A operators positions in one manual exchange to4 B operators cord circuits in another manual exchange, primary and secondary selector switches 'at the exchange in which said Boperators switchboard is located, trunk lines extending between said exchanges seizable by the A operators to extend calls, said trunk lines terminating in said primary selectors, means in said primary selectors operated responsive to the seizure thereof by an A operator over any one of said trunk lines for extending the trunk line used through said seized primary selector to one of said secondary selectors to seize the same, said secondary selectors having access to said B operators cord circuits, means in said seized secondary selector operated responsive to the seizure thereof for extending the said trunk line through said seized secondary selector to an idle cord circuit of one of said B operators positions, and means in said cord circuit operated responsive to the extension of said trunk line thereto for identifying that cord circuit by means of a signal, for preventing the seizure of said cord circuit by any other secondary selector, for preventing the seizure of the seized seconda-ry switch by any other prii, mary selector, and for maintaining the primary and secondary selector used in extending the trunk line to the cord circuit in seized condition.

6. In a telephone system, a plurality of A operators positions, a B operators position, cord circuits at said B operators position, selectors over which said A operators extend connections having access to said cord circuits, means in each of said cord circuits operated responsive to the extension of a connection to any one of them from said A operators via one of said selectors for preventing further seizure oi said one cord circuit by any other of said selectors, means common to all of said cord circuits operated during the time said B operator is setting up the connection received over said one cord circuit for preventing any other connections from said A operators from being received at said B operators position. '7. In a telephone system, a plurality of switches, a chain circuit including all of said switches, a resistance in each of said switches included in said chain circuit, a normally deenergized relay connected to said chain circuit, means` in each of said switches for shunting its associated resistance out of said chain circuit, said common relay energizing when a predetermined number of resistances have been shunted out of said chain circuit by said switches, and means controlled by said common relay for preparing an automatic stepping circuit foreach of said switches.

8. In a telephone system including an A operators position and a B operators position, trunk lines interconnecting said positions, A operators means for extending calls over said trunk lines, cord circuits at said B operators position, cord selecting means terminating each of said trunk lines, cord determining means interposed between each of said cord selecting means and each of said cord circuits for preselecting the cord circuits for each of said selecting means, and means at said B operators position operated after a call is received over one of her cord circuits for preventing the selection of preselected cord circuits by any of said cord selecting means until that call is extended while permitting any of said cord determining means to preselect other cord circuits at her position.

v9. In a telephone system, a B operators position, a plurality of cord circuits at said position,

a plurality of groups of non-numerical switches, each of the switches ini each of said groups having access to a different cord circuit, means for extending a call, via one ofrsaid switches and the cord circuit individual to the group of switches in which said one switch is located, to said position, and means responsive to the extension of said call to said position for preventing the extension of further calls to said position via any of the other switches in said groups of switches until that call is extended.

10. In a telephone system, a plurality of switches, a like plurality of associated wiper sets, bank contacts over which the wipers of said switches extend connections, a plurality of operators cord circuits multipled to the bank contacts of each of said switches, each of said switches having access to said cord circuits via said wipers and bank contacts, means for seizing any one of said switches to operatively connect with one of said cord circuits via an associated wiper set, each of said wiper sets including a test wiper and an auxiliary test wiper, means in the connected cord circuit operated responsive to a connection for extending circuits to any of said switches having test wipers and auxiliary test wipers of the wiper sets engaging bank contacts to which the selected cord is multipled to prevent the seizure of any other of said switches and to prepare stepping circuits for such switches, and means responsive when said last-mentioned circuits are extended via both of said test wipers to a predetermined number of said switches for controlling said stepping circuits to disconnect their associated wiper sets from the bank contacts to y:

which said connected cord circuit is multipled.

11. In a telephone system, a plurality of switches, a like plurality of associated wiper sets,

bank contacts over which the wipers of said switches extend connections, a plurality of operators cord circuits multipled to the bank contacts of each of said switches, each of said switches having access to said cord circuits via said wipers and bank contacts, means for seizing any one of said switches to operatively connect with one of said cord circuits via an associated wiper set, each of said wiper sets including a test wiper and an auxiliary test wiper, means in the connected cord circuit operated responsive to a connection for extending circuits to any of said switches having test wipers and auxiliary test wipers ofthe wiper sets engaging bank contacts to which the selected cord is multipled to prevent the seizure of any other of said switches and to prepare stepping circuits for such switches, and means responsive when said last mentioned circuits are extended via both of said test wipers to a predetermined number of said switches for controlling said stepping circuits to disconnect their associated wiper sets from the bank contacts to which said connected cord circuit is multipled, said last mentioned means also effective responsive to some of said predetermined number of switches disconnecting associated wiper sets from multiples of said connected cord to prevent other switches of said predetermined number from disconnecting their associated wiper sets from multiples of said connected cord.

12. In a telephone exchange system, a iirst operators position, calling jacks therefor, a trunk finder directly connected to each of said jacks, a second operators position, cord circuits at said second operators position, preselecting secondary selector switches connected to idle cord circuits, said secondary selector switches accessible by way of bank contacts of said nders, means responsive when the operator at said first position extends a connection by plugging into one of said jacks for controlling the associated iinder switch to extend the connection by way of its bank contacts to any secondary selector switch that has preselected an idle cord circuit, and means operated in the secondary selector switch to which the connection is extended for further extending the connection through to said preselected cord circuit,

13. In a telephone exchange system, a rst operators position, calling jacks therefor, a trunk nder directly connected to each of said jacks, a second operators position, cord circuits at said second operators position, preselecting secondary selector switches connected to idle cord circuits, said secondary selector switches accessible by way of bank contacts of said finders, means responsive when the operator at said rst position extends a connection by plugging into one of said jacks for controlling the associated nder switch to extend the connection by way of its bank contacts to any secondary selector switch that has preselected an idle cord circuit, means operated in the secondary selector switch to which the connection is extended for further extending the connection through to said preselected cord circuit, and means common to all of said cord circuits for placing a busy potential by way of said preselecting secondary selectors on the banks of said finder switches to prevent any of said iinder switches from operatively connecting with any of said cord circuits, when one of the cord circuits is being used to extend a connection.

14:. In a telephone system, a group of cord circuits, a preselecting switch temporarily associated with each of the cord circuits of said group, an incoming trunk for each of said preselecting switches, hunting switches for selecting said trunks and associated preselecting switches to extend connections to any one of said cord circuits, means responsive to the extension of a connection to one of said cord circuits for preventing the seizure of another trunk by any of said hunting switches, a second group of cord circuits, and means in said preselecting switches operated responsive to the extension of the connection to said one cord circuit for controlling said preselecting switching to select cord circuits in said second group of cord circuits to thereby permit said hunting switches to extend connections only to cord circuits in said second group of cords.

l5. In a telephone system, a plurality of incoming lines, a primary selector terminating each of said incoming lines, primary trunk lines accessible to said primary selectors, a preselecting secondary selector switch individual to each of said primary trunk lines, secondary trunk lines accessible to said secondary selectors, cord circuits individual to each of said secondary trunk lines, said primary trunks characterized as unselectable by the presence of a potential and characterized as selectable by the absence of a potential, means for operating said primary switch over an incoming line to thereby select a primary trunk line characterized by the absence of said potential and connected via a preselecting secondary switch to an idle cord circuit, and means in said preselected cord circuits for controlling the application of the potential to said primary trunks when said cord circuits are not selectable.

16. In a telephone system, a plurality of operators positions, cord circuits individual to each of said positions, switches adapted to preselect idle cord circuits at said positons, means operated reponsive to incoming calls for nding and extending the calls to preselected cord circuits, means at an operators position operated when said position is vacated for preventing the iinding means from connecting with preselected cord circuits at said position, means common to said switches operated only when a predetermined number of switches are engaging cord circuits at a vacated position by controlling a portion of said predetermined number of switches to preselect idle cord circuits at an attended position.

1'7. In a telephone system, a plurality of cord circuits, rotary switches and associated bank contacts, said switches arranged to preselect said cord circuits by way of said bank contacts,

means for seizing said switches to extend connections to said cord circuits, means common to said cord circuits operated as long as an operator is answering a connection received over one of said cord circuits for busying all of said cord circuits to thereby prevent said seizing means from extending connections to said cord circuits, means common to saidv cord circuits operated when the operator tending said cord circuits is absent for busying all of said cord circuits to thereby prevent said seizing means from extending connections to any of said cord circuits and for controlling a certain percentage of said rotary switches to disconnect from the cord circuits that are not attended.

18. In a telephone system, a plurality of operators positions, a plurality of cord circuits at each of said positons, means individual to each position for preventing incoming calls from being received by any cord circuit thereat while an operator is extending a call received over one of the cord circuits, a second individual means at each position for busying all of the cord circuits at a position during the time that said position is vacated to thereby prevent any incoming calls from connecting with a cord circuit at said vacated position, distributor switches normally engaging idle cord circuits at said positions, and means, in the switches connected to cord circuits of a vacated position, operated by the second individual means for controlling a percentage of the switches connected to cord circuits of a vacated position to cause them to engage idle cord circuits at attended positions.

19. In a telephone system, a plurality of operators positions, a plurality of cord circuits for each of said positions, a plurality of switches connected to cord circuits at both of said positions, means at each position for busying all the cord circuits thereat during the time that the position is vacated and for removing the busy condition from the cord circuits thereat when the position is again attended, means common to said switches for controlling a percentage of the switches connected to busied cord circuits of said vacated position to select idle cord circuits at the attended positions, and means common to all positions operated momentarily when said vacated position is again attended for controlling switches connected to cord circuits at the remaining positions to connect with idle cord circuits at the again attended position.

JOHN WICKS. 

